1. Field of the Invention
The present invention relates to high moment material for a shield or pole piece layer in a magnetic head, such as a giant magnetoresistive (GMR) head and, more particularly, to the manufacturing of high moment Fe--Al--N--O laminated film using N.sub.2 O as the reactive gas for the shield or pole piece layer in the magnetic head.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk with write and read heads that are suspended by a suspension arm above the rotating disk. An actuator swings the suspension arm, placing the write and read heads over selected circular tracks on the rotating disk. The write and read heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating. When the disk rotates, air is swirled by the rotating disk adjacent the ABS of the slider, causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at the air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field, or the lack thereof, writes information in tracks on moving media, such as in circular tracks on a rotating disk.
In recent read heads, a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. A spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor. When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve.
There a number of materials that may be used in the construction of the magnetic head, the most common being NiFe. GMR wafer processing requires annealing in a magnetic field parallel to the hard axis of the shields (of the read head) and the poles (of the write head) for optimal performance of the GMR sensor. In the present process, there are typically at least three high temperature anneals that are performed, for both hardbake and pole pieces. These anneals are typically performed at around 232.degree. C. for 400 minutes. These hard axis anneals are known to reduce the anisotropy field, H.sub.k of plated NiFe. Other materials considered for write head and shield materials, such as FeN, FeAlN, FeTaN, FeZrN and FeRuN, reduce or even switch H.sub.k in conventionally processed laminated films. By careful control of the substrate bias, sputter pressure, nitrogen content and other conditions, films can be fabricated which retain magnetic anisotropy after hard axis annealing, but in all cases there is still some decrease in H.sub.k and increase in H.sub.ch after hard axis annealing. This loss of intrinsic anisotropy causes unfavorable domain structures to form, which in turn causes instability in the read sensor in a read head shield application or reduction in high frequency permeability in a write head pole application.
There are shield layers (S1, S2) and pole piece layers (P1, P2) in close proximity of the read sensor. Because of the proximity, it is important that the layers be magnetically stable. In order to achieve this, the shield or pole layers are formed by plating or sputter deposition in the presence of a magnetic field that is parallel to the ABS in the plane of the shield or pole layer. The field orients the easy axis (e.a.) of the shield or pole layer in the direction of the field, namely parallel to the ABS and in the plane of the shield or pole layer. This orientation also means that the magnetic domains in the shield or pole layer in the vicinity of the sensor are also aligned with their longitudinal axes parallel to the ABS in the plane of the shield or pole layer. It is important that these domains retain their orientation as formed and not move around when subjected to extraneous fields such as fields from the write head or fields from the rotating magnetic disk. When these magnetic domains move, noise is generated which is referred to in the art as Barkhausen noise. This noise seriously degrades the read signal of the read head. Further, if the magnetic domains do not come back to their original position, the shield or pole layer exerts a differently oriented field on the free layer of the spin valve sensor. This changes the magnetic bias on the free layer causing read signal asymmetry.
Nickel iron (NiFe), with a composition of approximately Ni.sub.81 Fe.sub.19 (wt. %), has been typically employed for the shield or pole layers. Nickel iron (NiFe) is a soft magnetic material that provides good shielding of the spin valve sensor from magnetic fields except within the read gap where signals are sensed by the sensor. Nickel iron (NiFe) also has near zero magnetostriction so that after lapping the head to form the ABS there is near zero stress induced anisotropy. Unfortunately, however, nickel iron (NiFe) has a low intrinsic magnetic anisotropy (H.sub.K). Intrinsic magnetic anisotropy is the amount of applied field required to rotate the magnetic moment of the layer 90 degrees from an easy axis orientation. The intrinsic magnetic anisotropy of nickel iron (NiFe) is 2-5 oersteds (Oe). After the first shield layer (S1) and second shield layer (S2) layer are formed, they are subjected to unfavorable magnetic fields that are required in subsequent processing steps. The insulation layers of the insulation stack are hard baked in the presence of a magnetic field, that is directed perpendicular to the ABS, for the purpose of maintaining the magnetic spins of the antiferromagnetic pinning layer in the spin valve sensor oriented in a direction perpendicular to the ABS. After completion of the head, the head is subjected to an additional anneal in the presence of an external magnetic field directed perpendicular to the ABS for the purpose of resetting the spins of the pinning layer perpendicular to the ABS. These annealing steps reduce the anisotropy field of nickel iron (NiFe) to very low values of 0-1 Oe.
The field typically employed for maintaining the spins of the pinning layer during hard bake of the insulation stack is about 1500 Oe and the field for resetting the spins of the pinning layer after completion of the head is about 13 kG. Because of the low intrinsic magnetic anisotropy of a nickel iron (NiFe) shield layer, the aforementioned anneals in subsequent processing can cause the easy axis and the magnetic domains of the shield layer to switch their orientation such that they are no longer parallel to the ABS. The magnetic field present in these anneals reduces or destroys the intrinsic anisotropy field that was created in the nickel iron (NiFe) when it was originally formed and may create an anisotropy field perpendicular to the ABS. This is a very unfavorable position for magnetic domains of a shield layer. When the shields are subjected to perpendicular fields from the write head during the write function or perpendicular fields from the rotating magnetic disk the magnetic domains will move. This causes Barkhausen noise which degrades the read signal and causes a potential change in biasing of the spin valve sensor which results in read signal asymmetry.
In general, it is desirable to minimize the reduction of H.sub.k that occurs in hard axis annealing, and particularly desirable that this can be done while simultaneously achieving low hard axis coercivity, H.sub.ch, and near zero magnetostriction, .lambda., for the process conditions used for the GMR wafers. Accordingly, there is a strong felt need for a material for the first shield layer (S1), the second shield (S2) and first and second pole piece layers (P1 & P2) that will remain stable after being subjected to heat and magnetic fields employed in subsequent process steps.